1. Field of the Invention
The present invention relates to a process for producing an aluminum support for a planographic printing plate which can remarkably reduce raw material costs and which enables high image-quality printing, and to an aluminum support for a planographic printing plate and a planographic printing master plate. Also, the present invention relates to a process for producing an aluminum support for a planographic printing plate having excellent printability with regard to resistance to severe ink soiling and blanket soiling, an aluminum support for a planographic printing plate and a planographic printing master plate. Furthermore, the present invention relates to an aluminum support for a planographic printing plate which can remarkably reduce raw material costs and which has fine crystal grains, giving high image quality and printing durability.
2. Description of the Related Art
Generally, an aluminum support for a planographic printing plate (hereinafter simply called xe2x80x9csupportxe2x80x9d or xe2x80x9cplanographic printing plate-use aluminum supportxe2x80x9d as the case may be) is produced by carrying out, for example, a roughening treatment for one or both surfaces of an aluminum plate. Also, a planographic printing master plate is produced by disposing, for example, a light-sensitive layer on the support. In most of the above supports, the surface of the aluminum plate is treated by anodic oxidation after the surface-roughening treatment to improve the wear resistance of the planographic printing plate during printing. Also, the surface of the light-sensitive layer is occasionally provided with fine irregularities called a matt layer to shorten a time required for vacuum adhesion during plate-making. The planographic printing master plate produced in this manner is made into a planographic printing plate through a plate-making process including image exposure, developing and washing with water. As a method for image exposure, a method in which a lith film on which an image is printed is made to adhere to the surface of the support and irradiated with light to thereby make an image portion different from a non-image portion, a method in which an image portion or a non-image portion is directly written by a method using a laser, or a method in which an image is projected thereby making the image portion different from the non-image portion can be used.
Also, after a developing treatment performed after the image exposure, the undissolved portion of the light-sensitive layer serves as an ink-receptor and forms an image portion, and, at a portion where the light-sensitive layer is dissolved and removed, the surface of the aluminum or the anodic oxide film underneath is exposed externally and serves as a water-receptor and forms a non-image portion. After developing, a hydrophilicizing treatment, gum drawing and a further burning treatment may be carried out according to the need.
Such a planographic printing plate is attached to a cylindrical print drum of a printer and ink and damping water are supplied to the print drum. This results in the ink sticking to the lipophilic image portion and the water sticking to the hydrophilic non-image portion. The planographic printing plate works to transfer the ink of the image portion to a blanket drum and then an image is printed from the blanket drum on paper.
However, there are cases where ink is occasionally stuck to the non-image portion in dot or ring patterns, giving rise to the problem that dot-like or ring-like spots on paper (severe ink spots) are caused resultantly.
In order to restrain the occurrence of such severe ink spots and the like, it has been considered to adopt a method using an aluminum alloy material containing a virgin metal and predetermined additive element components as an aluminum alloy material to be used for the support. However, these materials have the drawback that the costs of these materials themselves are high.
It has also been considered to adopt a method using waste aluminum which is generated in aluminum factories and of which the alloy composition is known. Although the method has the advantage that yield from raw materials is improved, this waste aluminum is not cheap.
On the other hand, if the adhesion between the image portion and the light-sensitive layer is insufficient when the ink of the image portion is transferred to the blanket drum and the image is printed from the blanket drum on paper, this pose the problem that a lower number of copies can be printed before termination of printing. As methods for improving the adhesion between the image and the light-sensitive layer, a method in which an intermediate layer is interposed between the aluminum alloy plate and the light-sensitive layer and a method in which the aluminum alloy plate is uniformly roughened are known.
An amino acid or its salts (e.g., alkali metal salts such as Na salts and K salts; ammonium salts; hydrochlorides; oxalates; acetates; and phosphates) as disclosed in Japanese Patent Application Laid-open (JP-A) No. 60-149491, amines having a hydroxyl group or salts thereof (e.g., hydrochlorides; oxalates; and phosphates) as disclosed in JP-A-60-232998 or compounds having an amino group and a phosphonic acid group or salts thereof as disclosed in Japan Patent Application No. 63-165183 may be used for an undercoating intermediate layer. Also, compounds having a phosphonic acid group as disclosed in JP-A-4-282637 may be used for the intermediate layer. Moreover, it is known that after treatment using an alkali metal silicate is carried out, a high molecular compound containing an acid group and an onium group as disclosed in JP-A-9-264309 (JP-A-11-109637) is used for the intermediate layer. However, the method in which an intermediate layer for improving adhesion is formed between the roughened surface and the light-sensitive layer, as a matter of course, poses the problem of increased production costs for the formation of the intermediate layer.
On the other hand, it is known that in order to carry out a surface-roughening treatment uniformly, alloy components which are contained in the aluminum alloy and adversely affect the formation of a rough surface should be limited.
Many proposals have been disclosed as a method for limiting alloy components. Technologies concerning, for example, the material of JIS 1050 are disclosed in JP-A-59-153861, JP-A-61-51395, JP-A-62-146694, JP-A-60-215725, JP-A-60-215726, JP-A-60-215727, JP-A-60-215728, JP-A-61-272357, JP-A-58-11759, JP-A-58-42493, JP-A-58-221254, JP-A-62-148295, JP-A-4-254545, JP-A-4-165041, Japanese Patent Application Publication (JP-B) No. 3-68939, JP-A-3-234594, JP-B-1-47545 and JP-A-62-140894 by the inventors of the present invention. Also, JP-B-1-35910, JP-B-55-28874 and the like are known. Technologies concerning the material of JIS 1070 are disclosed in JP-A-7-81264, JP-A-7-305133, JP-A-8-49034, JP-A-8-73974, JP-A-8-108659 and JP-A-8-92679 by the inventors of the present invention.
Technologies concerning Alxe2x80x94Mg type alloys are disclosed in JP-B-62-5080, JP-B-63-60823, JP-B-3-61753, JP-A-60-203496, JP-A-60-203497, JP-B-3-11635, JP-A-61-274993, JP-A-62-23794, JP-A-63-47347, JP-A-63-47348, JP-A-63-47349, JP-A-64-61293, JP-A-63-135294, JP-A-63-87288, JP-B-4-73392, JP-B-7-100844, JP-A-62-149856, JP-B-4-73394, JP-A-62-181191, JP-B-5-76530, JP-A-63-30294 and JP-B-6-37116 by the inventors of the present invention. Also, JP-A-2-215599 and JP-A-61-201747 are known.
Technologies concerning Alxe2x80x94Mn type alloys are disclosed in JP-A-60-230951, JP-A-1-306288 and JP-A-2-293189 by the inventors of the present invention. Also, JP-B-54-42284, JP-B-4-19290, JP-B-4-19291, JP-B-4-19292, JP-A-61-35995, JP-A-64-51992, U.S. Pat. Nos. 500,972, 5,028,276 and JP-A-4-226394 are known.
Technologies concerning Alxe2x80x94Mnxe2x80x94Mg type alloys are disclosed in JP-A-62-86143 and JP-A-3-222796 by the inventors of the present invention. Also, JP-B-63-60824, JP-A-60-63346, JP-A-60-63347, EP223737, JP-A-1-283350, U.S. Pat. No. 4,818,300, BR1222777 and the like are known.
Technologies concerning Alxe2x80x94Zr type alloys are disclosed in JP-B-63-15978 and JP-A-61-51395 by the inventors of the present invention. Also, JP-A-63-143234, JP-A-63-143235 and the like are known. As to Alxe2x80x94Mgxe2x80x94Si type alloys, BR1421710 and the like are also known.
However, these alloys pose restrictions on alloy materials and have the disadvantages that freedom of selection of materials is decreased and an expensive virgin metal and predetermined additive alloy elements which are expensive are required.
These various alloys are usually manufactured by melting raw materials containing aluminum as a major component, adding predetermined metals to the molten raw materials to prepare a molten bath of an aluminum alloy having predetermined alloy components and, in succession, performing purifying treatment for the aluminum alloy molten bath, followed by casting. As the purifying treatment, a flux treatment for removing unnecessary gases such as hydrogen in the molten bath; a degassing treatment using Ar gas, Cl gas or the like; filtering using a so-called rigid media filter such as a ceramic tube filter or a ceramic foam filter, a filter using alumina flakes or alumina balls as a filter material, or a glass cloth filter; or a treatment comprising a combination of the degassing treatment and filtering is performed. These purifying treatments are preferably performed to prevent defects caused by foreign substances such as non-metallic inclusions and oxides in the molten bath and defects caused by the gas melted into the molten bath.
As aforementioned, a molten bath which has been purified is used to perform casting. Casting methods include methods using a fixed mold, represented by the DC casting method, and methods using a drive mold, represented by the continuous casting method.
In the case of the DC casting method, the cooling rate is designed to be in a range from 1 to 300xc2x0 C./sec. In the course of the process, a part of the aforementioned alloy component elements are melted as a solid solution in aluminum and components which cannot be melted as a solid solution form various intermetallic compounds and remain in the resulting ingot. In the DC casting method, an ingot having a plate thickness of 300 to 800 mm can be produced. The ingot is subjected to facing according to a usual method wherein a surface layer with a thickness of 1 to 30 mm and preferably 1 to 10 mm is cut. Thereafter, the ingot is subjected to a soaking treatment according to the need. The soaking treatment ensures that among the intermetallic compounds, unstable compounds are changed to more stable compounds and some of the intermetallic compounds are melted as solid solution in the aluminum. Here, the remainder of the intermetallic compounds are afterwards decreased in diameter and dispersed in hot rolling and cold rolling processes but there is no further change in types. Namely, such remaining intermetallic compounds are left in the aluminum alloy plate to be used as a support for a planographic printing plate.
There are cases where, before, after or during cold rolling, a heat treatment called annealing is carried out. In this case, a part of the elements melted as solid solution occasionally precipitate as intermetallic compounds or precipitates of single elements. These precipitates are also left in the aluminum alloy plate.
The aluminum alloy plate which is finished in a given thickness (0.1 to 0.5 mm) by cold rolling may be bettered in flatness by using a remedy machine such as a roller leveler or a tension leveler.
As the casting method, a continuous casting method may also be used. For this method, a twin-roll continuous casting method, represented by the Hunter method or 3C, method or a twin-belt continuous casting method, represented by a belt caster such as the Hazellee method or a block caster such as the Alusuisse method, may be used. In the case where, for example, a twin-roll is used, the cooling rate is designed to be in a range from 100 to 1000xc2x0 C./sec. On the other hand, in the case where a twin-belt is used, the cooling rate is designed to be in a range from 10 to 500xc2x0 C./sec. In both methods, the aluminum alloy plate is made to have a given thickness (0.1 to 0.5 mm) by a rolling treatment comprising cold rolling or a combination of hot rolling and cold rolling after the casting operation is finished. Also, at this time, a heat treatment may be carried out optionally. The aluminum alloy plate which is finished in a predetermined thickness by cold rolling may be improved in flatness by using a remedy machine such as a roller leveler or a tension leveler. These continuous casting methods are characterized by the advantage that the running cost is lower than for the DC casting method because the facing process required in the DC casting method can be omitted.
Here, as aluminum used as the raw material, generally, an aluminum ingot having a purity of 99.7% or more, which is called virgin metal, is used or scrap aluminum which is generated in aluminum manufacturing factories and of which the alloy composition is known is used. An aluminum alloy, called the mother alloy, containing predetermined elements is added and a metal ingot consisting of predetermined metal elements is added to manufacture an aluminum alloy material having desired alloy components.
However, the aluminum alloy material containing the virgin metal and predetermined additive element components has the disadvantage that the cost of the material itself is high. Also, the case where scrap aluminum which is generated in aluminum manufacturing factories and of which the alloy composition is known is used has a merit in the point that the yield from the raw material is improved, but is not at all inexpensive.
In regard to the problem that the cost of the raw material is high, a method in which only an aluminum ingot having aluminum in a content of 99.7% or more is used and it is unnecessary to add a mother alloy or metal ingot containing predetermined elements is proposed in JP-A-7-81260. Also, a method in which used planographic printing plates or planographic printing plates which are made inferior in the course of the process are reused as the raw material of the aluminum plate is proposed in JP-A-7-205534.
Even these methods, however, do not bring about large effects because the aluminum ingot itself having aluminum in a content of 99.7% or more is not inexpensive and it is difficult to consistently secure the used planographic printing plates as a raw material.
To solve such problems, there is the idea that materials whose alloy composition is uncontrolled as the raw material, namely, scrap materials containing various impurities or ground metals called secondary metals (recycled metals) which have a commercial price lower than that of the virgin metal and contain many impurity elements be used. However, these materials are not controlled as to the alloy composition and therefore have not been used at all as the raw material of a planographic printing plate for which a high quality appearance of a treated surface and high printability are required. Particularly, because various intermetallic compounds and precipitates are generated in these materials, there are the drawbacks that defects of the anodic oxide film tend to be caused resulting in considerable inferiority in resistance to severe ink soiling and, in addition, the presence of the intermetallic compounds and the precipitates gives rise to causes such as blanket soiling which deteriorates printability. Also, uniform surface-roughening cannot be accomplished, causing the problem of insufficient adhesion to the light-sensitive layer and inferior printing durability.
Further, it is essential for a reduction in energy consumption in the future to make full use of low purity aluminum plates as aluminum supports for planographic printing plates with a view to suppressing energy consumption in the recycling of used aluminum.
It is an object of the present invention to provide a process for producing a high quality planographic printing plate-use aluminum support, the process being remarkably reduced in raw material costs by using, as the raw material, a material whose alloy composition is not controlled, namely, a scrap material containing various impurities or a ground metal known as a secondary metal (recycled metal) which has a commercial price lower than that of virgin metal and contains many impurity elements, and being restricted in the occurrence of severe ink soiling and blanket soiling, and also to provide a planographic printing plate-use aluminum support and a planographic printing master plate. Another object of the present invention is to provide a planographic printing plate-use aluminum support which is free from the necessity for provision of an expensive intermediate layer and the necessity of a uniform roughening treatment, which uses very inexpensive raw materials and which has high adhesion to a light-sensitive layer and excellent printing durability.
The aforementioned objects are attained by the following means.
A first aspect of the present invention is a process for producing an aluminum support for a planographic printing plate, the process including the steps of: (a) preparing an aluminum plate; (b) disposing said aluminum plate in an aqueous acidic solution; and (c) electrochemically surface-roughening said aluminum plate using an alternating current, wherein a ratio QC/QA of a cathode-time quantity of electricity of said aluminum plate QC to an anode-time quantity of electricity of said aluminum plate QA is from 0.95 to 2.5.
A second aspect of the present invention is an aluminum support for a planographic printing plate formed by electrochemically surface-roughening an aluminum plate in an aqueous acidic solution using an alternating current, wherein a ratio of cathode-time quantity of electricity of said aluminum plate during said surface-roughening to anode-time quantity of electricity of said aluminum plate during said surface-roughening is from 0.95 to 2.5.
A third aspect of the present invention is a planographic printing master plate having at least a positive-type or negative-type light-sensitive layer on an aluminum support for a planographic printing plate, wherein said aluminum support for a planographic printing plate is formed by electrochemically surface-roughening an aluminum plate in an aqueous acidic solution using an alternating current, wherein a ratio of cathode-time quantity of electricity of said aluminum plate during said surface-roughening to anode-time quantity of electricity of said aluminum plate during said surface-roughening is from 0.95 to 2.5.
A fourth aspect of the present invention is an aluminum support for a planographic printing plate including an aluminum alloy plate having an aluminum content of 95 to 99.4 mass %, on which at least a surface-roughening treatment and an anodic oxidation treatment have been performed.